Some new designs of mobile communication devices-such as smart phones, tablet computers, and laptop computers-support two Subscriber Identity Module (SIM) cards that provide users with access to two separate mobile telephony networks. Examples of mobile telephony networks include GSM, TDSCDMA, CDMA2000, and WCDMA. Example multi-SIM mobile communication devices include mobile phones, laptop computers, smart phones, and other mobile communication devices that are enable to connect to multiple mobile telephony networks. A mobile communication device that includes two SIM cards and connects to two separate mobile telephony networks using two separate radio frequency (RF) communication circuits is termed a “dual-SIM-dual-active” (DSDA) device.
Because a DSDA device has two separate RF communication circuits or “RF chains,” each subscription on the DSDA device may use its associated RF chain to communicate with its mobile network at any time. However, because of the proximity of the antennas of the two RF chains included in a DSDA communication device, the simultaneous use of the two RF chains may cause one RF chain to desensitize and thus interfere with the ability of the other RF chain to receive transmission.
Receiver desensitization (“de-sense”), or degradation of receiver sensitivity, may result from noise interference from a nearby transmitter. In particular, when two radios are close together with one transmitting on the uplink and the other receiving on the downlink, the feedback from the transmitter may be picked by the receiver. As a result, the received signals may become corrupted and difficult or impossible to decode. Further, feedback from the transmitter can be detected by a power monitor that measures the receive signal, which would cause the mobile device to falsely determine the presence of a cell site. In particular, receiver de-sense may present a challenge in multi-radio devices, such as devices configured with multiple SIMs, due to the necessary proximity of transmitter and receiver.
In general, mobile device radio receivers may have filters to reduce interference from a simultaneous transmit signal. In order to be effective, a transmit filter needs to be positioned in the radio circuitry after the signal is amplified, but that requires a filter that can handle high power levels, and such filters are expensive. As such, previous communication system designs are inadequate to mitigate the effects of de-sense in DSDA devices. Thus, there is a need for a method for managing the de-sense received on one of the RF chains in a DSDA device.